The present invention relates to cellular coal products produced from coal in powder and to their methods of production. Products utilizing the coal-based porous products are also described.
ASTM standards DD5515-97, xe2x80x9cStandard Test Method for the Determination of Swelling Properties of Bituminous Coalxe2x80x9d and D720-91 xe2x80x9cStandard Test Method for Free Swelling Index of Coalxe2x80x9d both define conditions for measuring the inherent property of coals to xe2x80x9cswellxe2x80x9d upon heating in an uncontrolled combustion situation. Hence, the propensity of coal to swell is well known in the prior art. To the best of our knowledge, however, no one has attempted to take advantage of this property of coals to swell by controllably xe2x80x9cswellingxe2x80x9d a coal product to obtain a highly useful, low density, porous carbon product.
Similarly, very sophisticated processes have been developed for the production of cellular foamed carbon products. Such processes often involve the use of blowing agents and the application of very high pressures in the fabrication process, and many use highly sophisticated starting materials. These materials, while very lightweight and demonstrating superior strength, tend to be relatively costly, either due to the nature of their starting materials and/or the complexity of their fabrication processes.
There exists a wide and varied class of requirements for low-density materials in the construction, aerospace, transportation, metal processing and other industries for which low-density materials are constantly being developed. Many of these materials exhibit properties such as fire resistance that make them uniquely suited to their end use application. In many applications, however, the aforementioned relatively high cost, low-density materials cannot be used because the final application will simply not justify their relatively high cost.
Accordingly, it would be most desirable if a relatively low cost, low-density material demonstrating many of the desirable characteristics of the aforementioned products, such as fire resistance, were available.
It is therefore an object of the present invention to provide a relatively low cost, low density product that is suited to application in the construction, aerospace, transportation, metal processing and other industries where such properties are desired.
It is another object of the present invention to provide a simple and low cost method for the production of such products.
According to the present invention there are provided coal-based cellular or porous products, also referred to herein as xe2x80x9ccarbon foamsxe2x80x9d, having a density of preferably between about 0.1 g/cm3 and about 0.8 g/cm3 and most preferably between about 0.3 and about 0.4 g/cm3 that are produced by the controlled beating of coal particulate preferably up to xc2xd inch in diameter in a xe2x80x9cmoldxe2x80x9d and under a non-oxidizing atmosphere. According to a specifically preferred embodiment, the starting material coal has a free swell index as determined by aforementioned ASTM D720 test of between about 3.5 and about 5.0. According to further preferred embodiments of the present invention, the starting material coal exhibits one or more and preferably all of the following set of properties: 1) a volatile matter content (dry, ash-free basis) of between about 35 and about 45% as defined by ASTM D3175, xe2x80x9cTest Method for Volatile Matter in the Analysis of Coal and Cokexe2x80x9d; 2) a fixed carbon (dry basis) between about 50 and about 60% as defined by ASTM D3172, xe2x80x9cPractice for Proximate Analysis of Coal and Cokexe2x80x9d; 3) a Gieseler initial softening temperature of between about 380xc2x0 C. and about 400xc2x0 C. as determined by ASTM D2639, Test Method for Plastic Properties of Coal by the Constant-Torque Gieseler Plastometerxe2x80x9d; 4) a plastic temperature range above about 50xc2x0 C. as determined by ASTM D2639; 5) a maximum fluidity of at least 300 ddpm (dial divisions per minute) and preferably greater than about 2000 ddpm as determined by ASTM D2639; 6) expansion greater than about 20% and preferably greater than about 100% as determined by Arnu Dilatation; 7) vitrinite reflectance in the range of from about 0.80 to about 0.95 as determined by ASTM D2798, xe2x80x9cTest Method for Microscopical Determination of the Reflectance of Vitrinite in Polished Specimens of Coalxe2x80x9d; 8) less than about 30% inert maceral material such as semifusinite, micrinit, fusinite, and mineral matter as determined by ASTM D2798; and 9) no significant oxidation of the coal (0.0 vol % moderate or severe oxidation) as determined by ASTM D 2798 and non-maceral analysis. (The desirability of each of these individual properties and their order of preference will be further elaborated below.) The porous product or carbon foams thus produced, preferably as a net shape or near net shape, can be machined, adhered and otherwise fabricated to produce a wide variety of low cost, low density products, or used in its preformed shape as a filter, heat or electrical insulator etc. Such cellular products, without further treatment and/or the addition of strengthening additives have been shown to exhibit compressive strengths of up to about 4000 psi. at densities of between about 0.3 and about 0.4 g/cm3 or 19 to 25 lb/ft3. Other interesting properties of such materials are tensile strengths of between about 300 and 1000 psi, shear strengths in the range of about 300 psi and impact resistances of between about 0.3 and 0.4 ft-lbs./in2 as measured by Izod impact on a notched, 0.5 square inch cross-section sample. Impregnation with appropriate materials or the incorporation of various strength improving additives can further increase the compressive, tensile and other properties of these cellular materials. Treatment by carbonization or graphitization yields cellular products that can be used as electrical or heat conductors.